Napoli host Barcelona, Dortmund target a famous comeback and more besides – there are eight last-16 places on the line on Thursday and the ties are almost all delicately poised.
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It is all to play for in the knockout round play-off second legs, and the abolition of the away goals rule means all eight ties could yet go either way.
Enterprise Rent-A-Car presents UEFA.com's guide to the stand-out stories.
No away goals rule
Following the recommendation of the UEFA Club Competitions Committee and the UEFA Women's Football Committee, the UEFA Executive Committee approved in June a proposal to remove the so-called away goals rule from all UEFA club competitions.
With the decision to remove this rule, ties in which the two teams score the same number of goals over the two legs are no longer decided on the number of goals scored away but by two 15-minute periods of extra time and, if necessary, a penalty shoot-out.
Will Malen step into the breach?
"It is a great night, but only a great night," warned Giovanni van Bronckhorst after Rangers' rousing 4-2 triumph in Dortmund. The Dutchman may have been looking out of the corner of his eye at a certain Erling Haaland, glowering in the stands during the first leg as the Yellow Wall crumbled.
The Norwegian did not travel with the squad to Glasgow on Wednesday, but Sunday's 6-0 victory over Mönchengladbach proved that BVB can perform without him. Donyell Malen was among the scorers at the weekend and, generally, when the Dutch youngster gets one he goes on a run.
What are the knockout round play-offs?
The UEFA Europa League knockout round play-offs have been introduced for the first time this season. There are 16 teams involved: the eight runners-up from the UEFA Europa League group stage and the eight third-placed teams from the UEFA Champions League group stage.
The eight winners advance to the round of 16 draw on Friday (the eight group winners have already qualified for this); the eight play-off losers will no longer be involved in 2021/22 European competition.
Can Barcelona rediscover their finishing touch?
There were more than a few concerned faces at the Camp Nou when Piotr Zieliński put Napoli ahead in the first leg, forlorn looks that collectively formed to spell out "not again". Xavi Hernández's side allayed those fears with an impressive second-half showing, yet despite 21 shots they scored only one – and that was a penalty.
"The goals will come," Xavi vowed, and his players duly delivered on Sunday when Pierre-Emerick Aubameyang struck a hat-trick in a 4-1 win at Valencia. Napoli's shaky form provides further hope, but the Italian side aren't riding high in Serie A for no reason.
Who awaits in the last 16?
Crvena zvezda (SRB)
Eintracht Frankfurt (GER)
Spartak Moskva (RUS)
West Ham (ENG)
The draw takes place at 12:00 CET on Friday, streamed live here.
17 & 24 February: Knockout round play-offs
25 February: Round of 16 draw
10 & 17 March: Round of 16
18 March: Quarter-final & semi-final draws
7 & 14 April: Quarter-finals
28 April & 5 May: Semi-finals
18 May: Final (Estadio Ramón Sánchez-Pizjuán, Seville)